Photographic material with improved silver covering power



3,408,199 PHOTOGRAPHIC MATERIAL WITH IMPROVED SILVER COVERING POWER Wilhelm Saleck, Schildgen, Karl Dinges, Cologne-Stammheim, and Erwin Miiller, Leverkusen, Germany, assignors to Agfa-Gevaert Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany N Drawing. Filed June 21, 1965, Ser. No. 465,769 Claims priority, application Germany, July 4, 1964,

5 Claims. (Cl. 96-114) The invention relates to photographic material with at least one silver halide emulsion layer having improved photographic characteristics. More particular the invention relates to a method for increasing the covering power of developed silver and improving the maximum density, contrast and speed of gelatino silver halide emulsions.

It is known that the covering power of developed silver in photographic layers can be increased by adding a variety of compounds. Addition of the compound produces a higher density for an equivalent concentration of silver halide, or, alternatively a considerable amount of silver is saved in instances where it is merely intended to obtain the same density.

It has been proposed to add polysaccharides and their derivatives for this purpose. These products are, however, of limited utility since the advantageous eflect cannot be obtained without concomitantly increasing uncontrollable fog and instability or tropical aging. The same holds true with polyvinyl pyrrolidone or N-alkylated polymethacrylamides which have also been used for this purpose.

The object of the present invention is to provide substances which increase the silver covering power of silver halide layers without, at the same time, producing any deterioration in the photographic properties.

Another object is to provide photographic silver halide emulsions demonstrating increased covering power of the developed silver.

It has now been found that silver halide gelatin emulsions of increased covering power of the developed silver and enhanced properties can be made by adding to the emulsions an effective amount of polymers or copolymers of derivatives of N-methylol methacrylamide or of N- methylol acrylamide.

These polymeric products are characterized by a content of at least 15 mol percent of units of the following formula:

R L. ,l

in which X represents the groups 7 h V -CH2O-Rz o CH2-0i J-Rz R represents an alkyl radical preferably containing up to 3 carbon atoms and R represents a methyl group or hydrogen.

United States Patent 0 3,408,199 Patented Oct. 29, 1968 with short-chain aliphatic alcohols having up to 5 carbon atoms, in particular methyl esters, methacrylonitrile or acrylonitrile. Other copolymerisable monomers, for example, ethylene, propylene, butylene, vinyl acetate, vinyl ethers, particularly those whose aliphatic ether grouping contains up to 4 carbon atoms, may also be used for the copolymerisation.

The only condition which has to be met is that the resulting products should be soluble in water and compatible with gelatin and should not exert any harmful influence on the photographic properties of the photosensitive layers. Their activity is based on the presence of the units corresponding to the above formula which they have to contain in the concentration specified.

The polymeric products to be employed in accordance with the invention preferably have a molecular weight up to 100,000. The molecular weight is not critical. The most suitable molecular weight range may be determined by simple comparison tests.

The silver covering power is very considerably increased by the polymers according to the invention, so that, even when added in relatively small quantities, they produce marked eflects. In addition, they exhibit the surprising property of eliminating fogging and, to some extent, of increasing sensitivity. In this respect it is particularly remarkable that the fog-inhibiting effect even occurs under extreme conditions, for example on prolonged storage in a heating chamber at 60.

The polymers to be used in the manner according to the invention may be prepared by known processes. Useful methods are described, for example, in Die makromolekulare Chemie, vol. 57 (1962), pages 27-51.

The preparation of a homopolymer and of a copolymer are described in the following:

Polymethacrylamide-N-methylol methylether Methacrylamide-N-methylol methylether:

C H3 H2C=l J-C O.NH.OH2.0 CH3 Following the addition of 6 g. of hydroquinone, 300 g. of paraformaldehyde and 636 g. of finely powdered methacrylamide (MP. -106 C.), 48 g. of powdered sodium methylate are gradually introduced while stirring well at 40 C. into 7.5 litres of carbon tetrachloride to form an alkaline liquid. The product is then heated for 1 hour to 50 to 55 C., during which time the methacrylamide gradually disappears and the methylol compound precipitates as an oily layer on the carbon tetra-chloride. The carbon tetra-chloride is distilled off at 40 C., and the upper layer is poured while stirring into 3.6 litres of methanol, into which 48 g. of I-ICl gas had previously been introduced. There is slight spontaneous heating and, on completion of introduction, the solution still has a pH value of about 2. It is left to react for one hour at 40 C., after which any hydrochloric acid still present is neutralized by the addition of g. of anhydrous, finely powdered soda. Stirring is continued until the solution shows an alkaline reaction, after which it is filtered to remove the precipitated sodium chloride and any soda still present. The methanol is then concentrated by evaporation in vacuo. The remaining oil boils at 86 C./0.8 mm. Yield: 781 g.=8l% of the theoretical.

Polymerisation: 830 g. of benzene and g. of the above monomer are initially introduced into a 3-necked flask equipped with a thermometer, stirring mechanism and reflux condenser. After the air in the flask has been displaced with nitrogen, 0.85 g. of azodiisobutyrodinitrile are added while stirring, and the mixture is heated at 70 C.

Polymerization is finished after 5 to 6 hours at 70 C., the polymer precipitating as a white powder. After cooling, 100 g. of acetone are added and the mixture is suction-filtered.

After drying at 50 C. in vacuo, 156 g. of a white powder with a K-value of 38 to 40 are obtained (92% of the theoretical).

Copolymers of methacrylamide N methylol methylether: Copolymeri'sation is performed in analogous manner except that the benzene is replaced by a mixture of 415 g. of benzene and 415 g. of ethylacetate.

Yield: copolymer with acrylamide (mol ratio 1:1) 94%, K-value: 63.5; copolymer with methacrylamide (mol ratio 1:1) 93% K-value: 31.8 [according to Fikentscher,

Cellulosechemie, vol. 13, page 5 8 (1932)].

The polymers according to the invention may be added to the light-sensitive silver halide emulsion layers or to any auxiliary layers such as intermediate or protective layers. They may be added at any stage in the preparation of the emulsion or to the casting solutions for the layers. They are used in the form of aqueous solutions containing 10 to by weight of the polymer. The colorless polymer powders are generally soluble in warm water at a temperature of 30 to 50 C.

The polymers according to the invention are added to the layers in quantities varying from 5 g. to 140 g., preferably from 10 g. to 50 g. per mol of silver halide. When used in emulsion layers, from 5 to 50% of the gelatin may be replaced. The most suitable concentrations in which they are used depend upon the desired effect, the silver content of the emulsion and the type of silver halide used. The most favourable concentration may be determined in known manner by some comparison tests.

The photographic emulsions in which the compounds according to the invention are used may be chemically sensitized in the usual way, for example, by polyethylene oxides, quaternary ammonium compounds or sulfur compounds, as described, for example, in the book by Mees entitled The theory of the Photographic Process (1954), pages 149 to 169.

The emulsions may be further chemically sensitized by the addition of noble metal compounds, such as gold, rhodium, palladium, ruthenium, iridium and platinum compounds. The emulsions may also be sensitized by reducing agents, for example, stannous salts or polyamides.

Also suitable for this purpose are optically sensitized emulsions which contain the conventional cyanine, merocyanine or rhodacyanine sensitizing dyes. Dyes which may be used are described in F. M. Hamers book The Cyanine Dyes and Related Compounds, Interscience Publishers, 1964.

The emulsions may be stabilized with known compounds such as mercury compounds, triazoles, for example, mercapto-phenyltriazoles, or azaindenes which are described, for example, in the article by Birr in the Journal Wiss. Photographic vol. 47 (1952), pages 2 to 28.

The binding agent used for the layers is preferably gelatin which may be completely or partly replaced by other water-permeable film-forming colloids, such as alginic acid and its derivatives, for example, alkalimetal salts or esters preferably with lower aliphatic alcohols, polyvinyl pyrrolidones, starch or carboxyalkyl cellulose such as carboxymethylcellulose.

EXAMPLE 1 a hardening agent, for example, one of the hardening agents described in German Patent Specification No. 872,153, and is then divided up into a number of samples. One sample is used for comparison, whilst 50 ml. and ml. per liter, respectively, of a 20% by Weight aqueous solution of polymethacrylamide N methylolmethyl ether are added to second and third samples.

All three emulsion samples are applied onto transparent cellulose acetate support, forming layers of equal thickness, and are then dried. I

By increasing the content of the polymer of the invention, the last two samples contain less silver halide per m9 of the light-sensitive layer. After exposure in a sensitometer behind a grey /2 step wedge, the three samples are developed for five minutes at 20 C. in a developer of the following composition:

7 G. p-Methylaminophenol 3.5 Sodium sulfite (anhydrous) 60 Hydroquinone 9 Soda (anhydrous) 40 Potassium bromide 3.5 Water to make up 1 liter.

The results of the tests are shown in Table 1:

TABLE 1 Silver coating, g./m.

Amount, Sensitivity, Maximum ml. de

Sample g. density 4 Foggingv 1 Standard type.

The photographic properties of the same emulsions after three days storage in a heating chamber at 60 C. are shown in the following Table 2:

TABLE 2 Sensitivity, deg.

Maximum Fogging density 1 Standard.

EXAMPLE 2 TABLE 3 Silver coating, g./m.

Maximum density Amount Sensitivity,

addiad, deg. Fogging 1 Standard.

EXAMPLE 3 50 ml. of a 20% by weight solution of polymethacrylamide-N-methylohnethylether is added to a silver halide emulsion of the type used in Example 1, after which the emulsion is poured onto a support of polyethylenglycol terephthalate as described above.

The light-sensitive emulsion layer is coated with a protective layer containing as sensitizer a polyethylene oxide having a molecular weight of 4500 (Sample G). In another sample, a mercury stabilizer (0.4 mg./l. of mercury thiazole chloride) is added to the emulsion layer before casting (Sample H). The results given in Table 4 show that the increase in the effective speed is accompanied by an increase in the covering power. Above all, there is hardly any increase in fogging, which is not usually the case when these substances are used in highly sensitive emulsions.

TABLE 4 Amount Sensitivity, Maximum Specimen adgled, deg. density Fogging None 3. 0. 50 +1. 3 8. 1 0. 07 50 +0. 3 3. 1 0. 03

1 Standard.

If this material is additionally stabilized with the mercury stabilizer (Sample H), very slight fogging occurs, despite the increased sensitivity. It is readily apparent from these examples that the compounds of the present invention are also effective when combined with chemical sensitizer and other stabilizers.

EXAMPLE 4 To a silver halide emulsion as described in Example 1, are added 50 ml. of a 20% by weight solution of a copolymer of 75% by weight of N-methylmethacrylamide and 25% by weight of acrylic acid, according to Belgian Patent specification No. 620,515. The material is processed as described in the previous examples.

The results of the comparison test are in the following table and show the deleterious effect of this copolymer on the photographic properties. In comparison with the standard Sample A, density is about the same and the silver covering power is increased. The material, however, cannot be used in practice owing to the high degree of fogging.

What is claimed is:

1. A light-sensitive material comprising at least one light sensitive silver halide emulsion layer having improved covering power of developed silver which contains a polymeric product with at least 15 mol percent of units of the following formula:

Lan

in which X represents a substituent selected from those having the formulae R represents a member of the group consiiting of hydrogen and methyl and R stands for an alkyl radical containing up to 3 carbon atoms.

2. A light-sensitive material comprising at least one light-sensitive silver halide emulsion layer having im proved covering power of developed silver which contains a polymeric product consisting of a homopolymer of a monomer of the group consisting of an ester of N-methylolacrylamide the ester grouping of which has up to 4 carbon atoms, an ether of N-methylolacrylamide the ether grouping of which has up to 3 carbon atoms, an ester of N-methylol methacrylamide the ester grouping of which has up to 4 carbon atoms and an ether of N-methylol methacrylamide the ether grouping of which has up to 3 carbon atoms.

3. A light-sensitive material comprising at least one light-sensitive silver halide emulsion layer having improved covering power of developed silver, which contains a polymeric product with at least 15 mol percent of units of the group consisting of ethers of N-methylol acrylamide, the ether grouping of which has up to 3 carbon atoms, esters of N-methylol acrylamide, the ester grouping of which has up to 4 carbon atcms, ethers of N-methylol methacrylamide, the ether grouping of which has up to 3 carbon atoms or esters of N-methylol methacrylamide, the ester grouping of which has up to 4 carbon atoms and up to mol percent of polymerized units of a monomer of the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, N-alkylacrylamide, Naalkylrnethacrylamide, acrylic acid esters the ester grouping of which has up to 5 carbon atoms, methacrylic esters the ester grouping of which has up to 5 carbon atoms, acrylonitrile, methacrylonitrile, ethylene, propylene, vinyl acetate, or vinyl alkyl ethers, the ether grouping of which has up to 4 carbon atoms.

4. A photographic material as defined in claim 2, wherein the polymeric product is polymethacrylamide-N- methylol methyl ether.

5. A photographic material as defined in. claim 3, wherein the polymeric product is a copolymer of methacrylamide-N-methylol methyl ether and acrylamide or methacrylamide.

References Cited UNITED STATES PATENTS 2,533,166 12/1950 Jones 26089.7 2,593,888 4/1952 Jones 96-114 XR 3,069,263 12/1962 Haas 961 14 XR 3,178,295 4/1965 Minsk et al. 96-l14 3,178,296 4/1965 Minsk et al. 961l4 3,341,332 9/1967 Nakajima et al. 961l4 XR NORMAN G. TORCHIN, Primary Examiner.

R. H. SMITH, Assistant Examiner. 

1. A LIGHT-SENSITIVE MATERIAL COMPRISING AT LEAST ONE LIGHT SENSITIVE SILVER HALIDE EMULSION LAYER HAVING IMPROVED COVERING POWER OF DEVELOPED SILVER WHICH CONTAINS A POLYMERIC PRODUCT WITH AT LEAST 15 MOL PERCENT OF UNITS OF THE FOLLOWING FORMULA: 